Diesel engines commonly include diesel particulate filters (DPFs) to reduce emission of soot and other particulate matter (PM) from diesel fuel combustion. However, DPFs increase drivetrain cost, complexity, and weight, and can reduce engine performance and fuel economy. Increasing the fuel oxygen content is one method that may reduce the PM emission levels such that a DPF may be foregone. Introduction of a higher oxygen-containing fuel into the engine combustion chambers may promote more uniform combustion and reduce fuel-rich regions within the combustion chambers, where soot and PM tend to form.
However, the inventors herein have recognized various issues with the above approach. Namely, a fuel oxygen content corresponding to a large enough reduction in PM to meet engine emissions standards (without a DPF) depends on many factors, including the design of the engine and combustion system. Accordingly, combustion of a fuel having a higher fuel oxygen content may overly penalize or may unnecessarily reduce the fuel economy of an engine operating under conditions where PM emissions are inherently lower.
In one example, the issues described above may be at least partially addressed by a method comprising: positioning a pressure control valve (PCV) at an outlet of a fuel rail; positioning a volume control valve (VCV) at an inlet of a high pressure pump; and in response to an exhaust particulate matter (PM) level deviating from a target PM level, adjusting a fuel ratio of a first fuel and a second fuel delivered to an engine, and opening one of the PCV and the VCV.
In another example, a method for an engine may comprise: estimating a fuel oxygen content of fuel delivered to the engine; and in response to the fuel oxygen content deviating from a target fuel oxygen content, adjusting a flow of a first higher oxygenated fuel from a first fuel tank and a flow of a second lower oxygenated fuel from a second fuel tank to a fuel rail of the engine, and opening one of a pressure control valve (PCV) and a volume control valve (VCV), wherein opening the PCV purges fuel from a fuel rail upstream from the engine, and opening the VCV purges fuel from a high pressure fuel pump upstream from the fuel rail.
In another example, a vehicle system may comprise: an engine; a fuel system, including a first fuel tank, a second fuel tank, a pressure control valve (PCV) positioned between a fuel rail and a blend fuel tank and a volume control valve (VCV) positioned between a high pressure fuel pump and the blend fuel tank; and a controller, with executable instructions to, in response to an exhaust particulate matter (PM) level deviating from a target PM level, purge fuel from the high pressure fuel pump to the blend fuel tank by opening the VCV, purge fuel from the fuel rail to the blend fuel tank by opening the PCV, and adjust a fuel oxygen content delivered to the engine by adjusting a fuel flow rate from one of the first fuel tank, the second fuel tank, and the blend fuel tank.
In this way, the fuel oxygen content may be adjusted to achieve the technical result of maintaining a PM at or below a target level without a DPF over a broad range of engine designs and operating conditions, while maintaining fuel economy. Furthermore, by adjusting an opening of one or more of the VCV, and the PCV, fuel may be more rapidly purged from the high pressure side of the fuel system (e.g., high pressure pump, fuel rail) and fuel lines leading to the high pressure pump and the fuel rail, thereby making adjustments to fuel oxygen content can be more responsive, further reducing PM emissions and increasing fuel economy. Further still, CO2 emissions may be reduced due to reduced exhaust system back pressure as a DPF may be eliminated, which in turn can increase engine power and torque, and may enable engine downsizing. Further still, the technical result of eliminating the DPF from the exhaust system lowers manufacturing costs and may enable further significant cost reductions for other related engine components such as the NOx aftertreatment or the EGR system. Eliminating the DPF from the exhaust system also eliminates the need for DPF regeneration which further reduces PM and CO2 emissions and increases fuel economy. Further still, in a vehicle system engine comprising a DPF, the methods and systems described herein may be utilized to reduce frequency of DPF regeneration, thereby reducing both fuel consumption and PM emissions, and prolonging a life of the DPF.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.